A member of the Yemeni forces backed by a Saudi-led coalition takes position in the outskirts of the rebel-held port city of Hodeida, Yemen, June 3, 2018. (Najeeb Almahboobi/Epa-Efe/Rex/Shutterstock)

Yemeni forces backed by the United Arab Emirates have rapidly advanced to less than 10 miles from the rebel-held seaport of Hodeida, threatening to attack despite U.S. and United Nations warnings against undermining hoped-for peace talks and exacerbating Yemen’s humanitarian ­crisis.

“It’s a very fluid situation,” a senior U.S. official said after talks in Riyadh, the Saudi Arabian capital, last week with Emirati and Saudi officials. “We have really advised them to proceed with extreme caution, not to make a move on the city or the port for all sorts of reasons.”

“We’re trying to stay the Emirati hand right now,” the official said.

U.N. envoy Martin Griffiths, after discussions with all parties over the past several weeks, plans to present a new peace proposal on Friday to resolve the conflict, which has killed at least 10,000 civilians, displaced millions and left much of the population suffering from famine and disease.

Thousands have already fled Hodeida, a city of about 600,000 on the Red Sea through which most of the humanitarian aid to Yemen flows. It has been controlled since late 2014 by the Houthis, Yemeni rebels who have been fighting for more than three years against forces loyal to the Saudi- and Emirati-backed government.

“We are extremely concerned about the situation around Hodeida. . . . Obviously, increased fighting there would unleash even more internally displaced people,” Stéphane Dujarric, spokesman for U.N. Secretary General António Guterres, said last week.

The UAE has not asked for additional American military support to bolster a Hodeida offensive, according to U.S. and Emirati officials. U.S. defense officials said there are no plans to reduce current levels of assistance, which includes intelligence and aerial refueling for Saudi and Emirati warplanes.

Emirati ground forces are about nine miles from Hodeida, and the UAE government told U.S. officials that they will not move forward. At the same time, however, the UAE says it has no control over the Yemeni government forces that it has trained and assisted.

The UAE has “coordinated with the U.S., with the [U.N.] envoy. Everyone is in line with [the] strategy,” said a senior Arab official who spoke on the condition of anonymity, on both name and country. “No one is being surprised.”

Part of that strategy involves pressuring the Houthis into accepting new peace negotiations; the UAE has also proposed turning the port over to international control.

The U.S. official, who spoke on the condition of anonymity to discuss private diplomatic talks, said the Emiratis “reaffirmed” last week that their forces “are not planning at this time” to participate in a Hodeida offensive but that “the situation could change . . . if there is an attack on them or some sort of provocation from inside the city meant to draw them in.”

The official said the Emiratis are “the key players there,” despite claims that they have no control. If the rebels unilaterally attack approaching Yemeni forces, “we might very well ask Hadi and the Emiratis to intervene.”

Abed Rabbo Mansour Hadi is the internationally recognized president of Yemen. A Saudi-led coalition, including the UAE and other Persian Gulf states, launched a military intervention to restore him to power after he fled a Houthi force that seized Sanaa, the Yemeni capital, in 2014.

The coalition has pounded Houthi-held areas — including Sanaa and Hodeida — for years. Saudi forces have primarily carried out the airstrikes, which human rights groups, and many in the U.S. Congress, charge have caused most of the civilian deaths in the conflict. Lawmakers have repeatedly tried to restrict U.S. military sales and assistance to the coalition.

The Obama administration withheld the sale of precision-guided missiles to Saudi Arabia amid wavering U.S. support and concern about the humanitarian situation. The administration rejected an Emirati request in late 2016 for increased assistance for an air and sea attack against Hodeida, about 140 miles from the landlocked capital.

President Trump approved the missile sale, and Defense Secretary Jim Mattis asked him to lift the Obama-era restrictions and provide “limited” additional support for Saudi and Emirati operations.

Mattis also asked for approval of the rejected Hodeida operation, including additional surveillance, intelligence and operational assistance.

The Hodeida attack never took place, and U.S. officials later appeared cool toward the idea of expanding the U.S. mission in Yemen.

But the missile approval and Mattis’s request for additional assistance signaled the administration’s intention to move aggressively against Iran. Echoing Saudi and Emirati allegations, the administration has accused Iran of training, arming and directing the Shiite Houthis in a proxy war to increase its regional clout against the Persian Gulf’s Sunni monarchies.

In particular, it has cited threats to international shipping in the area and said that the Iranians are transporting missiles to the Houthis through the Hodeida port. In recent months, Houthi forces have fired missile barrages into Saudi Arabia.

As the humanitarian crisis worsened last year, however, Trump called on the coalition to “immediately” allow “food, fuel, water, and medicine to reach the Yemeni people who desperately need it.”

British Prime Minister Theresa May, after speaking with Trump early Monday, issued a statement saying they agreed on the need for a political solution in Yemen and the importance of countering “Iran’s destabilizing regional activity,” but “cautioned against any action that might increase the severe humanitarian suffering there.”

A White House statement on the call said Trump discussed Iran’s behavior in Yemen, but it did not mention political solutions or the humanitarian situation.

In a statement in Yemen over the weekend, however, a spokesman for the National Security Council said that “the United States has been clear and consistent that we will not support actions that destroy key infrastructure or that are likely to exacerbate the dire humanitarian situation that has expanded in this stalemated conflict.”

The Emiratis have long deployed ground forces in southern Yemen, where they have trained, armed and assisted government and allied fighters who have made gains over the past three months, retaking towns along the Red Sea and moving north toward Hodeida.

In Twitter postings over the weekend, Anwar Gargash, the UAE minister of state for foreign affairs, predicted “imminent” victory for coalition forces in the long-stalemated war, saying that the performance of Emirati troops has been “inspiring.” Gargash has met twice with Secretary of State Mike Pompeo since Pompeo took office in late April.

The coalition-backed Hodeida governor, Al Hassan Taher, said that Yemeni army troops were “advancing towards Hodeida and are working to encircle it from two directions: in the south and southeast with the aim of blocking any supplies to the [Houthi] militias” from Sanaa and other areas under their control.”

In remarks published Friday by the London-based newspaper Asharq Al-Awsat, Taher said that an exit route would be left for militants to flee the city.

Gregory Johnson, a Yemen scholar at the Arabia Foundation, called the Emirati government’s decision to hold back its forces a “fig leaf” for both the UAE and the United States. “The United States wants some deniability and they want the Emiratis to have some deniability,” he said.

The UAE-backed forces had encountered little resistance as they pushed toward the city, he said, but the prospect of an intense battle for Hodeida raised questions about the future of their alliance.

“These are groups that don’t all have the same long-term goals,” Johnson said. “They’re not necessarily on the same side, but they’re all against the Houthis at the moment.”

Correction: This article has been corrected to reflect that Secretary of State Mike Pompeo has met twice with United Arab Emirates Foreign Minister Abdullah bin Zayed Al Nahyan, and not with the UAE minister of state for foreign affairs.